Difficulties have been encountered in prior wellhead sealing assemblies in sealing between the exterior of the casing and the interior of the wellhead housing since the exterior of the casing may vary considerably in its dimensions. Additionally, extremely cold temperatures have made sealing with elastomers difficult because they contract very measurably in cold environments.
In one example of prior art a wellhead sealing assembly designed for sealing in the annulus between the first and second casings at the wellhead of a geothermal well, the sealing assembly includes a first ring with inner and outer seals mounted thereon and separate energizing rings which are actuated by screws extending vertically through a flange spanning the annulus above the sealing assembly. This structure is shown in U.S. Pat. No. 4,299,395.
Another example of a wellhead sealing assembly is shown in U.S. Pat. No. 2,768,841. The sealing assembly in this structure includes a base ring with a sealing ring above it and a top ring which has a tapered upper-outer surface engaged by tiedown screws extending through the wellhead housing in a radial direction.
The W. L. Todd et al U.S. Pat. No. 3,494,638 discloses a sealing assembly energized by radially extending tiedown screws and the seal ring includes an upper ring, a lower ring and a seal ring between them with screws initially loading the seal rings. A similar structure is shown in the J. W. Thatch U.S. Pat. No. 2,617,485.